Non-metallic -tank anti-leak, self-sealing coating

ABSTRACT

A differential-thickness, self-sealing, anti-leak, all-over coating for the outside surface of a fuel container formed of HDPE plastic material and characterized with differentiated high and low puncture-threat regions. The coating includes, for the high-threat regions, a plural-layer portion possessing (a) an inner, high-elastomeric layer bonded substantially directly to the overlying portion of the container wall&#39;s outer surface, (b) an intermediate, high-elastomeric layer including a population of embedded, liquid-fuel imbiber beads formed over the inner layer, and (c) an outer, high-elastomeric layer formed over the intermediate layer, and for the low-threat regions, a single-layer portion bonded substantially directly to the overlying portion of the container wall&#39;s outer surface, and having a single, high-elastomeric layer which joins in a bridging manner, and in a differential-thickness transition region, to each of the plural-layer portion&#39;s layers to form collaboratively therewith a fully enveloping, elastomeric, shrink-wrap jacket around the container.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application Ser. No. 60/751,477, filed Dec. 16, 2005, for “Non-Metallic-Tank Anti-Leak, Self-Sealing Coating”. The entire disclosure content of this prior-filed provisional application is hereby incorporated herein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

We have participated recently in the development of a specialized-form, protective, liquid-reaction, elastomeric, self-sealing, anti-leak coating structure and methodology which involves the spray-application of material to the outside of a liquid petroleum fuel container, such as a fuel tank, for implementing several different anti-leak sealing mechanisms—liquid-imbibing, three-dimensional material swelling, congealing, and elastomeric spring-back memory—that are effective to seal quickly against fuel leakage from a puncture wound, such as a bullet wound, in the wall of such a container/tank.

For background purposes, and because we incorporate in the practice of the present invention a layered coating structure having some similarity to the layer structure resulting from this previous development work, reference is here made to related, currently pending Regular U.S. patent application Ser. No. 11/067,525, filed Feb. 25, 2005, for “Projectile Barrier and Method”. In this regular patent application, the basic structure of a layered, three-layer protective coating of the type just above mentioned is quite fully described and illustrated, and thus reference is made herein to that application to provide the reader with relevant background information.

The mentioned, earlier coating-structure development took place in the context of protecting metallic-walled containers, such as steel-walled and aluminum-walled containers (which may also include pipelines), and we have now devised a new technique, and an associated, resulting, plural-layered coating, involving the spray-application of a self-sealing coating structure (of the general type described in the '525 patent application) to the outside of a similar kind of fuel-holding container, but one whose walls are made not of metal, but rather of a plastic material, and specifically of so-called HDPE (High Density Polyethylene) plastic material. Chemical bounding to such a material is very difficult, and traditional mechanical bonding is challenging and problematic, but we have devised a new approach which grows out of our earlier self-sealing work, to accomplish coating and protection of such a tank (container), utilizing, principally, several styles of non-traditional mechanical bounding, including shrink-wrap bonding.

The present invention involves this new HDPE plastic-container plural-layered coating, or coating structure, and its application to achieve unexpectedly strong mechanical bonding. This structure, and its application methodology, are illustrated and described herein in the setting of a military-vehicle HDPE plastic fuel tank, a setting wherein the invention has been found to offer particular utility.

The coating structure proposed is three-layered in nature with respect to plastic container-wall locations where penetration is expected possibly to occur, with this layered structure including (a) an inner layer made of a high-elastomeric material, such as the two-part product sold under the trademark TUFF STUFF® formed from blended, precursor products whose product designators are Numbers 60012 and 60058, made by Rhino Linings USA, Inc., of San Diego, Calif., (b) a second, intermediate layer which includes that same elastomeric material, and in which there is embedded a plurality of liquid(fuel)-imbiber, bead-like elements, such as those bearing the product designator IMB230300, made and sold by Imbibitive Technologies America, Inc. of Midland, Mich., and (c) a third, outer layer which, again, is made solely of the same two-part elastomeric material employed in the inner layer. Inasmuch as container/tank wound penetration is expected to occur, if at all, on the lateral sides and on the bottom of such a tank, these three coating layers are created only on these several tank/container sides. A thin layer of elastomer only is applied to the top side of the tank/container. This layer preferably forms a full continuum with the outer layer in the three-layer portion of the overall coating structure. The resulting container coating structure essentially completely envelopes the coated container, and thus fully “captures” the tank/container. Post-spray-on curing of the mentioned high-elastomeric material involves certain shrinkage, and this phenomenon results in the outer layer, as a whole, acting around a coated structure as a shrink-wrap jacket.

The various important features and advantages of the invention will become apparent as the detailed description which now follows is read in conjunction with the accompanying drawings.

DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a photographic side-elevation of a removed and isolated military-vehicle fuel tank which has been treated with an exterior, plural-layered coating in accordance with practice of the present invention.

FIG. 2 is a simplified, illustrative cross section taken generally across the long axis of the tank of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to both figures in the drawings, an HDPE plastic fuel tank, or container, is shown generally at 10 in these figures. Tank 10, as will be explained, has been coated on all but its top side by spraying thereonto, in accordance with practice of the present invention, a three-layer coating 12, including an inner layer 12 a, an intermediate layer 12 b, and an outer layer 12 c. These inner, intermediate and outer layers are made, as generally described above herein, variously of the two above-mentioned materials (high-elastomer, and liquid-imbiber beads seen at 13 in FIG. 2), with inner layer 12 a preferably having a thickness in the range of about 0.200-inches to about 0.280-inches, an intermediate layer 12 b having a thickness in the range of about 0.125-inches to about 0.160-inches, and outer layer 12 c having a thickness which results in an overall three-layer coating thickness of about 0.5-inches. Because of the fact that the upper side 10 a of tank 10 will not normally be exposed to a puncture threat, but in order, nonetheless, to provide a desired, completely enveloping protective coating for this tank, here we, on the upper side of the tank, apply a relatively thin, single layer 12 d of the high-elastomeric material alone, preferably with a thickness of about 0.150-inches. Layer 12 d is applied to form a full-continuum jacket around tank 10, in cooperation with outer (and lower) coating layer 12 c.

Thus layer 12 d effectively joins with the other areas of the tank coating structure of this invention to form a mechanical “wrapper” (effectively a shrink wrapper) around tank 10 to assist in furnishing a good, principally mechanical, bond, holding the entire coating structure in place on the surface of this tank which, as mentioned earlier herein, because of the tank's formation of HDPE material, is difficult to join to by a chemical bonding mechanism. In other words, we create a fully enveloping, shrink-wrap jacket of coating material, rather than just a material which is applied to certain selected tank/container surface areas, to achieve excellent and tenacious mechanical bonding.

In preparation for applying our self-sealing coating, two things are done preliminarily to prepare the outer surface of the HDPE tank material to receive mechanically bonded coating material. First, the outer tank surface is preferably scrubbed/scuffed with a rotary wire cup brush to roughen and texturize the surface, and to remove the usual “surface gloss” of this surface. Contrary to a concern that such roughening and texturizing might introduce stress-failure regions in the otherwise and normally intended smooth-surfaced HDPE structure, this roughening collaborates with subsequently applied coating material(s) actually to strengthen the HDPE material against failure, especially in the guarded-against possibility of a material puncture wound.

Next, in any suitable manner, a suitable adhesion-promoting (mechanical-bond-enhancing) primer is sprayed as a thin film onto the scuffed surface. A suitable primer is the two-part catalyzed product known as DPX-801 plastic adhesive primer made by PPG Industries of Strongsville, Ohio.

The overall coating of this invention, and its application, employ several important and collaborative mechanical mechanisms to achieve a suitable mechanical “bonding” with an HDPE surface, and ultimately with an overall sturdy mechanical bond with tank 10, per se. One mechanism is based upon, and relates to, surface roughening to provide a good gripping-surface topography for the subsequently contacting coating material of this invention. Another such mechanism involves the presence of the mentioned adhesion-promoting primer. A third mechanism results from the application of our layered coating in a completely enveloping, shrink-wrap manner regarding the outside of a tank/container. This third mechanism utilizes full envelopment, along with natural coating-material shrinkage, to achieve a good gripping association (i.e., a shrink-wrap association) between a tank/container surface and the coating material per se.

As was mentioned earlier, the self-sealing coating structure featured in this invention performs puncture-wound sealing via several cooperative approaches which were mentioned earlier herein. By preparing an HDPE container surface, roughened and texturized, as described above, covered with a film of an appropriate mechanical-bond-enhancing primer, and by producing an all-enveloping, cooperatively-layered coating structure as discussed, an extremely effective, and very well surface-bonded puncture-wound sealing arrangement may be easily, quickly, and relatively inexpensively, created.

Thus, a unique and specially protective anti-leak, self-sealing coating for an HDPE plastic fuel container, and a methodology for application of this coating, have been illustrated and described herein. This coating is easily and relatively inexpensively applied either as an initial coating before a tank/container is installed, for example in a vehicle, for use, or it may readily be retro-applied if and when desired. Utilizing tenacious mechanical bonding mechanisms as described, the proposed plural layer coating hugs the outer surface of such a plastic container, and in fact strengthens to over all container. Those who are skilled in the relevant art will no doubt appreciate certain variations and modifications which may be made to deal with various special applications, and it is intended that all such variations and modifications will come within the scope and spirit of the invention. 

1. (canceled)
 2. The coating of claim 4, wherein the outer surface of the container wall is a non-shiny, textured, roughened surface, and wherein the coating further includes a film of mechanical-bond-enhancing primer disposed between this roughened surface and the plural-layer and single-layer portions in said coating.
 3. (canceled)
 4. A self-sealing, anti-liquid-leak, all-over layer-based coating for a liquid petroleum fuel container having an outer wall which defines lateral, bottom and top sides of the container each with an outer surface formed of HDPE plastic material, said layer-based coating having, for different, respective ones of the mentioned sides in the container, different overall thicknesses, and respectively associated, different numbers of layer, said coating comprising for each of the lateral and bottom sides, a first, common-thickness coating portion possessing three layers including (a) an inner, high-elastomeric material layer applied substantially directly to the side and mechanically bonded thereto, (b) an intermediate layer formed over said inner layer including a combination of substantially the same high-elastomeric material employed in said inner layer and additionally a population of embedded, liquid-fuel imbiber beads, and (c) an outer layer applied over said intermediate layer and formed of substantially the same high-elastomeric material which is employed in said inner layer, and for the top side, a single, second-coating-portion, top-side layer formed of substantially the same high-elastomeric material employed in said inner and outer layers in said first coating portion, joining with each of said inner, intermediate and outer layers in said first coating portion, and together with said first coating portion's said outer layer forming an elastomeric, shrink-wrap continuum fully and effectively enveloping the container.
 5. A self-sealing, anti-liquid-leak, all-over layer-based coating for a liquid petroleum fuel container having an outer wall which defines lateral, bottom and top sides of the container each with an outer surface formed of HDPE plastic material, said layer-based coating having, for different, respective ones of the mentioned sides in the container, different overall thicknesses, and respectively associated, different numbers of layer, said coating comprising for each of the lateral and bottom sides, a first, common-thickness coating portion possessing three layers including (a) an inner, high-elastomeric material layer with a thickness lying selectively in the range of about 0.200-0.280-inches applied substantially directly to the side and mechanically bonded thereto, (b) an intermediate layer formed over said inner layer, having a thickness lying selectively in the range of about 0.125-0.160-inches and including a combination of substantially the same high-elastomeric material employed in said inner layer and additionally a population of embedded, liquid-fuel imbiber beads, and (c) an outer layer having a thickness lying selectively in the range of about 0.060-0.175-inches applied over said intermediate layer and formed of substantially the same high-elastomeric material which is employed in said inner layer, whereby the collective thickness of the selected-thickness inner, intermediate and outer layers in said first coating portion is about 0.5-inches, and for the top side, a single, second-coating-portion, top-side layer having a thickness of about 0.150-inches formed of substantially the same high-elastomeric material employed in said inner and outer layers in said first coating portion, joining with each of said inner, intermediate and outer layers in said first coating portion, and together with said first coating portion's outer layer forming an elastomeric, shrink-wrap continuum fully and effectively enveloping the container.
 6. The coating of claim 5, wherein the outer surface of the container wall is a non-shiny, textured, roughened surface, and wherein the coating further includes a film of appropriate mechanical-bond-enhancing primer disposed between this roughened surface and the plural-layer and single-layer portions layers in said coating. 